Hybrid Zwitterionic Hydrogels with Encoded Differential Swelling and Programmed Deformation for Small-Scale Robotics.

Stimuli-responsive shape-morphing hydrogels with self-healing and tunable physiochemical properties are excellent candidates for functional building blocks of untethered small-scale soft robots. With mechanical properties similar to soft organs and tissues, such robots enable minimally invasive medical procedures, such as cargo/cell transportation. In this work, responsive hydrogels based on zwitterionic/acrylate chemistry with self-healing and stimuli-responsiveness are synthesized. Such hydrogels are then judiciously cut and pasted to form hybrid constructs with predetermined swelling and elastic anisotropy. This method is used to program hydrogel constructs with predetermined 2D-to-3D deformation upon exposure to different environmental ionic strengths. Untethered soft robotic functionalities are demonstrated, such as actuation, magnetic locomotion, and targeted transport of soft and light cargo in flooded media. The proposed hydrogel expands the repertoire of functional materials for fabricating small-scale soft robots.

Programmable nanocomposites of cellulose nanocrystals and zwitterionic hydrogels for soft robotics.

Stimuli-responsive hydrogels have garnered significant attention as a versatile class of soft actuators. Introducing anisotropic properties, and shape-change programmability to responsive hydrogels promises a host of opportunities in the development of soft robots. Herein we report the synthesis of pH-responsive hydrogel nanocomposites with predetermined microstructural anisotropy, shape-transformation, and self-healing. Our hydrogel nanocomposites are largely composed of zwitterionic monomers and asymmetric cellulose nanocrystals. While the zwitterionic nature of the network imparts both self-healing and cytocompatibility to our hydrogel nanocomposites, the shear-induced alignment of cellulose nanocrystals renders their anisotropic swelling and mechanical properties. Thanks to the self-healing properties, we utilized a cut-and-paste approach to program reversible, and complex deformation into our hydrogels. As a proof-of-concept, we demonstrated the transport of light cargo using tethered and untethered soft robots made from our hydrogels. We believe the proposed material system introduce a powerful toolbox for the development of future generations of biomedical soft robots.

Light-Fueled Hydrogel Actuators with Controlled Deformation and Photocatalytic Activity.

Hydrogel actuators have shown great promise in underwater robotic applications as they can generate controllable shape transformations upon stimulation due to their ability to absorb and release water reversibly. Herein, a photoresponsive anisotropic hydrogel actuator is developed from poly(N-isopropylacrylamide) (PNIPAM) and gold-decorated carbon nitride (Au/g-C3 N4 ) nanoparticles. Carbon nitride nanoparticles endow hydrogel actuators with photocatalytic properties, while their reorientation and mobility driven by the electrical field provide anisotropic properties to the surrounding network. A variety of light-fueled soft robotic functionalities including controllable and programmable shape-change, gripping, and locomotion is elicited. A responsive flower-like photocatalytic reactor is also fabricated, for water splitting, which maximizes its energy-harvesting efficiency, that is, hydrogen generation rate of 1061.82 µmol g-1 h-1 , and the apparent quantum yield of 8.55% at 400 nm, by facing its light-receiving area adaptively towards the light. The synergy between photoactive and photocatalytic properties of this hydrogel portrays a new perspective for the design of underwater robotic and photocatalytic devices.

Effect of Interphase Properties on Isothermal and Non-isothermal Crystallization Behavior of Poly(lactic acid)/Acetylated Starch Blends.

The effect of interphase properties on the crystallization behavior of blends of poly(lactic acid) (PLA)/acetylated starch (AS) with different degrees of substitution (DSs) was investigated. Under isothermal crystallization conditions, the rate of crystallization was higher for PLA/DS0.5 and lower for PLA/DS1.5 and PLA/DS2.5 when compared to PLA. In contrast, non-isothermal crystallization behavior indicated a slower rate of crystallization of PLA/DS0.5 and a faster rate of crystallization of PLA/DS1.5 and PLA/DS2.5 compared to PLA at the highest cooling rate (5 °C/min). The potential relationship between crystallization behavior and interphase properties and interphase thickness and formation of rigid amorphous fraction in the interphase, was investigated. The formation of a rigid amorphous fraction in PLA/DS1.5 and a thick interphase in PLA/DS2.5 prevented the formation of crystals on the dispersed phase and interrupted the crystallization under isothermal conditions. Hydrogen bonding in the PLA/DS1.5 blend and hydrophobic interactions in the PLA/DS2.5 blend may facilitate the crystallization at high cooling rates under non-isothermal conditions. Small-angle X-ray scattering analysis revealed the presence of a smaller lamellar structure in PLA/AS blends. The largest amorphous phase among blends was observed for the PLA/DS1.5 blend, which can be attributed to the hydrogen bonding in the interphase region of this blend.

Effect of Oil Phase Transition on the Stability of Pickering Emulsions Stabilized by Cellulose Nanocrystals.

Emulsifier design is one of the key strategies in interfacial engineering for emulsion stability. In this study, cellulose nanocrystals (CNCs) were used as an interfacial stabilizer to improve the stability of coconut oil (CO)-in-water emulsions. A Pickering emulsion consisting of CO and water was optimized based on four parameters using the response surface methodology and the central composite design. The droplet coverage remained stable during the crystallization of the oil phase when the temperature was reduced below the melting temperature of CO. Fluorescent-labeled CNCs were used to monitor the partitioning of CNC at the O/W interface during the crystallization of CO. The Generation 6 polyamidoamine (G6 PAMAM) dendrimer covalently grafted on the surface of CNC was used as an intrinsic fluorescent dye. Since it displayed similar properties as the emulsifier, it could be used to monitor the CNC coverage on the oil droplets at various temperatures. The fluorescence micrographs showed that the emission of PAMAM CNCs at the O/W interface remained on both the liquid and solid CO droplets, confirming that oil crystallization did not affect the fluorescent CNC coverage on the oil droplets.

Interfacial Control of the Synthesis of Cellulose Nanocrystal Gold Nanoshells.

Cellulose nanocrystal (CNC) gold nanoshell was prepared using a polymer-coated CNC as a template. A seed-mediated shell growth approach (ex situ) was employed, gold nanoparticles (AuNPs) of two sizes were prepared, and the effect of the size of AuNP on the shell quality (smoothness, evenness, and continuity) was elucidated. Additionally, a novel one-pot synthesis approach (in situ) was evaluated for the preparation of the gold nanoshell, where polymer-coated CNCs with adsorbed ascorbic acid were used to reduce Au ions to form a metallic gold shell on CNC. The surface coverage was manipulated by adding different amounts of plating solutions. The formation and morphology of gold nanoshells were evaluated by zeta potential measurements, dynamic light scattering, UV-vis spectroscopy, and transmission electron microscopy (TEM). The catalytic performance of the CNC-gold nanostructures for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was governed by the surface area of gold shells.

Poly(lactic acid)/acetylated starch blends: Effect of starch acetylation on the material properties.

This study investigated the acetylation of starch to improve its processability and compatibility with poly(lactic acid). The temperature at the maximum rate of degradation increased by 3.2% for poly(lactic acid) blends containing acetylated starch degree of substitution 2.5 compared to the blend containing neat starch. A biphasic morphology with distinct dispersed phase was predicted and observed experimentally for all blends except the blend containing acetylated starch degree of substitution 3. Acetylated starch induced plasticization and nucleation for all degree of substitution. The blend containing acetylated starch degree of substitution 2.5 had higher tensile strength (26%), and toughness (29%) compared to the blend containing neat starch. The superior mechanical properties of the blend containing acetylated starch degree of substitution 2.5 are attractive for medical implant applications. The continuous microstructure and transparency characteristics of the blend containing acetylated starch degree of substitution 3 are attractive for packaging applications.

Starch-based nanocomposites: a comparative performance study of cellulose whiskers and starch nanoparticles.

A comparative performance study of cellulose whiskers (CW) and starch nanoparticles (SN) on plasticized starch (PS) reinforcement has been presented. In order to study the involved surface phenomena, CW and SN were extracted through acid hydrolysis using sulfuric acid to fulfill the similar surface groups and interactions. CW-filled and SN-filled nanocomposites were then prepared with relatively identical process to alleviate the effect of fabrication method for better comparison of CW and SN performance on PS reinforcement. Morphology of nanoparticles and their dispersion state in the corresponding nanocomposites were investigated by transmission electron microscopy and field emission scanning electron microscopy, respectively. X-ray diffraction was used for crystallography of nanocomposites and established the transcrystallization only in CW-filled nanocomposites. Nanocomposites comprising quasi-spherical SNs showed higher reinforcement in dynamic mechanical tests compared to the corresponding nanocomposites containing rod-like CWs, which were attributed to more efficient filler/filler and filler/matrix interactions originated from hydrogen bonding in SN-filled nanocomposites.